1. Field of the Invention
This invention relates to a method for making a silicon dioxide coating on a substrate made of glass, ceramics, a metal or an organic material.
2. Description of the Prior Art
It is widely carried out these days to coat the surfaces of various materials with silicon dioxide coatings. For example, it has been practiced for many years to reduce the reflection of a surface, e.g., a glass surface by applying an alternating multi-layered coating of titanium oxide films and silicon dioxide films on the surface. It is also practices extensively to form a silicon dioxide coating as a protecting film on the surface of a metal or alloy. Besides, when using an alkali metal-containing glass such as soda-lime glass or boro-silicate glass as liquid crystal display panel or solar battery substrate glass, the surface of such a glass is coated with silicon dioxide in order to avoid the elution of its alkali metal component or components. Prevention of the elution of alkali metal component or components from glass has become a technique particularly indispensable for the maintenance of service life of liquid crystal display devices or solar batteries. In addition, the insulative property of a silicon dioxide coating has recently been attracting engineers' and researchers' attention. There is an ever-increasing necessity to ensure insulation between conductive films in various electronic parts and devices, for example, by employing a structure of a conductive film/silicon dioxide film/conductive film.
A variety of techniques has heretofore been employed to make silicon dioxide coatings on glass surfaces, including the vacuum deposition, sputtering and CVD techniques. These conventional techniques are however accompanied by such drawbacks that the formation of silicon dioxide coatings is costly as these conventional techniques require expensive facilities and accessories and, besides, they can be applied to small substrates only. In the case of a silicon dioxide coating applied for electrical insulation, the thickness of the coating is generally required to be at least 5000 .ANG. in many instances. However, the conventional vacuum deposition, sputtering or CVD technique is suffering from a slow coating formation velocity and is thus accompanied by another problem that the treatment cost becomes significantly high for the formation of a silicon dioxide coating of 5000 .ANG. or thicker. Furthermore, such conventional techniques tend to develop non-uniformity in the thickness of coatings as the coatings become thicker, thereby imposing a limitation to the current trend toward larger substrates.